An all electric mobile refrigeration unit or refrigerated container uses an auxiliary generator set to power the unit when traveling by rail or road. That is, whereas, when such a unit is being transported on board ship it is provided electrical power by way of the ships power, but when the container is being transported by rail car or by truck, no such electrical power is available. Accordingly, electrical power is provided by way of a motor/generator set during such period.
Unlike a truck/trailer refrigeration system, which is integrated and includes an overall control system for controlling all of the various components including the refrigeration system and the generator, the engine/generator set in a refrigerated container is a stand alone unit which does not communicate with the refrigeration system. This problem is exacerbated by the fact that various types of refrigeration units will be electrically powered by such an engine/generator set, with each such refrigeration system having its own unique operating characteristics. Accordingly, heretofore, there has been no unifying control system for communicating between the refrigeration system and the engine/generator set.
For this reason, in order to ensure that sufficient power is being delivered to the refrigeration system, the engine/generator set has been operated at a single, relatively high, speed at all times, even though the refrigeration unit may be operating under light load conditions or even in an off condition if the load requirements have been met. In this regard, the applicants have made studies which indicate that such a unit is typically lightly loaded for a majority of the time (i.e. up to 70% or more). However, a relatively large engine has been required to provide the power at high load conditions such as for pull down. The unit is therefore oversized for lighter load conditions, thereby resulting in inefficient fuel use.